Disk type magnetic recordingreproducing apparatus



Jan. 9, 1951 F. E. DHUMY ETAL 2,537,557

DISK TYPE MAGNETIC RECORDING-REPRODUCING APPARATUS Filed May 5, 1945 s Sheets-Shet 1 INVENTORS F. E.d'HUMY R.J.WIS E ATTORNEY 1951 F..-E. DHUMY ETAL 2,537,657

} DISK TYPE MAGNETIC RECORDING-REPRODUCING APPARATUS Filed May 5, 1945 3 Sheets-Sheet 2' 42 35 i l 39 28 34 F G. 2 40/ 45 25 A 58 29 mlllllllllllllllllllllllll i I INVENTORS F. E. dHUMY RJ. WISE ATTORN EY Jan- 19 1 I F. Ev DHUMY ETAL 2,537,657

DISK TYPE MAGNETIC RECORDING-REPRODUCING APPARATUS Filed May 5, 1945 5 Sheets-Sheet a A R H H7 H6 -||5 H4 H9 5 A D F A D I F :26 125 12'4 ATTORNEY Patented Jan. 9, 1951 DISK TYPE MAGNETIC RECORDING- REPRODUC ING APPARATUS Fernand E. dHumy, scarsdale N. Y., and Raleigh J. Wise, Duneilen, N. J assignors to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Application May 5, 1945, SerialNo. 592,094

3 Claims.

1 This invention relates to magnetic recording and retransmitting apparatus, and more particularly to a facsimile telegraph exchange system.

in which .novel and improved recording devices at a central or. exchange station enable facsimile messages received over an incoming line to bev stored and retransmitted. over an outgoing line to theplace of destination or to another exchange office, without requiring the messages to be re.- produced in. facsimile at the. exchange station.

.In facsimile telegraph systems at present in use, the incoming messages from a calling patron or originating oflice are .received at the central stationrand are recorded there on an electrosensitive recording blank or in some'instances photographically on sensitized film, after which the. subject matter thus recorded has to be rescanned by a transmitting optical pickup device for retransmission to the called patron. or office of destination. This operation results in an appreciable loss in detail of the reproduced subject matter; there is also involved loss in time .in the retransmission of the messages, and the additional expense incurred by the use of electrosensitive recording paper orphotographic film necessar to record the messages for subsequent. retransmission. Moreover, th re is an undesirable lack of secrecy involved since the subject matter recorded on the blanks at the central station unavoidably is disclosed to. numerous persons attending the recording and retransmitting facsimile machines.

:One of the objects of the invention is to avoid the foregoing and other dis-advantages attendant to facsimile reception and retransmission at a central .or otherexchange office.

Another object is to provide suitable means for the reception and retransmission. of facsimile messages at an exchange station, without the necessity of reproducing the .messages in visual or readable form at such station.

An additional object is an improved recording element for receiving and storing the facsimile signals magnetically pending the retransmission.

thereof, which recording element may be usedrepeatedly for succeeding messages, and which facilitates handling and requires a minimum of manual attention and supervision.

, A further object is to girovide a simple and ef'-' from the following detailed description of two illustrative embodiments of the invention, taken in connection with the accompanying drawings,

in which:

Fig. 1 is a topplan view of a. facsimile recorder utilizinga magnetizable storing .and retransmitting element constructed in accordance with onei form of the invention;

Fig. v2 is a front View, in elevation, of the recorderofFig. 1; I

Fig. 3 is a view in elevation, taken along the.

line 3 -.3..of Fig. .1;

Fig 4. is. an enlarged fragmentary View taken.

along. the line 4-4 of Fig. 1, showing certain de.-

: tails of. the magnetic recording and reproducingv elements;

Fig. 5 is a fragmentary plan view of a modified form of recording and retransmitting element;

Fig. .6 is a sectional view taken along the line- 6--6 of Fig.5; and.

Fig- 7 schematically shows certain. inter-ofiice connections. which may be employed in a system.

of the character disclosed.

Referring particularly to'E'igs. 1 to 3 of the drawings, there isshowna supporting framework for the recordencomprising a base plate l0,. pref-" erably of metal, having secured thereto uprightstuds ;or posts-l l which rigidly support an upper plate or frame member 12. The posts may be fastened .to. the plates [0 and. I2 in any suitable manner, as by machine. screws l5, Fig. 1, which, pass through the plates and are screw-threaded into the adjoining ends of the supporting posts. The upper plate l2 carriesa turntable 1.6 rotatably mounted by means of anti-friction bearings Fig. .2. The turntable is driven by a motor ['8 mounted on the plate .Ifl, driving power being transmitted through a motor shaft .19, a reducing gear box 20, .and a .d'rivenshaft 2| to which the turntable issecured, as by a pin or screw 22.

Turntable I6 is adapted to carry a, magnetic recording and retransmitting plate .or disc 25 constructed in accordance with the invention, .and'

insuring positive rotation of the disc by the turntable.

One embodiment of the recording and repro-f ducing disc .25 .isillustrated in detail in ,Fig. 4.,

and comprises a plate of magnetizable steel having a spiral hill or ridge 26 cut or otherwise formed in the upper surface thereof, and preferably also having a similar spiral ridge iii formed in the undersurface thereof. ,Coacting with the spiral ridge is the recording and reproducing head comprising two electromagnets 28 connected in series. magnetic core 29 of relatively large cross-section having a free end of reduced cross-section positioned immediately adjacent to one of the tapered sides of the ridge 25, thereby to cause a high concentration of magnetic flux at the reduced end of each of the pole pieces for locall magnetizing, in the manner of a Poulsen wire, the immediately adjacent portions of the ridge 26 when facsimile or other signaling currents are passed through the coils of the magnets 28. The pole pieces of the magnets are maintained in proper position and spacing relative to the opposite sides of the ridge or hill 25 by means of a supporting guide.

member 3|, the guide member having depending therefrom two prongs or tines 32 which are received in the valley portions formed 'by the spiral ridge 26. These tines support the weight of'the recording and reproducing head and cause the reduced ends of the pole pieces to be spaced,

very close to the adjacent sides of the ridge 25 so as to provide a minimum length of. operating air. gap, whileat the same time preventing friction between the pole pieces and ridge during ro-' Each of the magnets has a tationof the disc 25. The tines 32 also cause the recording and reproducing head to track properly at all times as the spiral ridge is being scanned thereby during recording or reproducing operations.

The magnets 28 and guide member 3| are secured to the forward end'of a scanning arm 34, the rear end of which is pivotally mounted at a point 35, Figs. 1 to 3, to enable movement of the scanning head in a horizontal plane laterally across the face of the magnetizable disc 25 from the outermost rows 26a, Fig. 1, to the innermost rows 26b of the spiral ridg 26. The arm 34 also is .pivoted by a bearing 36 in such manner that the forward portion of the arm and the scanning head carried thereb may be, raised upwardly, as

indicated in dotted outline in Fig. 3, to facilitate insertion or removal of the magnetizable disc. The forward portion of the arm 34 preferably has a. longitudinal rib 39 to impart a desired strength and rigidity to the arm without unduly increasing.

thesize or weight thereof. At the pivotal point the arm may be rotatably mounted inany suitable manner. For example, and seen more clearly in Fig. 3, a supporting bracket member 46 is se cured, as by machine screws or bolts 4!, to an opposite portion l2a of the upper supporting plate member 12, the bracket carrying an adjustable pivotal screw 42. The rear of the arm 34 terminates in a bracket portion composed of a central vane 45 and flanged portion 45 secured to a stub shaft 41 which is rotatably mounted by anti-friction bearings 48 within the support lZa. Thus, during either a recording or reproducing operation, the tines 32 of the recording and reproducing head will track in the vales on either side of the spiral ridge 26 and cause the reproducer head to travel across the disc 25 to effect linear scanning at a ratedetermined by the rotational speed of the disc.

Preferably, and as seen in Figs. 2 to 4, a second scanning arm 5|] is provided to scan the rides on the underface of the magnetizable disc simulta-, neously with the upper scanning arm 34. This underside of the disc.

enables two messages to be recorded or retransmitted simultaneously, or one of the faces of the disc may be employed to record and retransmit synchronizing or other control signals to accompany the recorded message on the other face thereof, thereby insuring that the stylus or other reproducing means at a receiving station will scan the receiving record blank at the same rate as scanning was effected at the original transmitting station and in proper phase relation therewith.

The arm 50 carries at its forward end a reproducer head like that of arm 34. Arms 50 is mounted, by a pivoted bearing 55, to the bracket structure 45, 46, so that it moves directly beneath and in alignment with the arm 34 as scanning of both faces of the magnetizable disc proceeds. A con'tractile spring 54, Fig. 3, has one end secured to the arm 50 and its other end anchored to a rod 55 rigidly secured to the bracket structure 45, 45, and serves to resiliently urge the recording and reproducing head of the lower arm into opera: tive position with respect to the ridge 25 on the need be depressed onl a slight distance in order to disengage its scanning head from the under:

side of disc 25, this clearance being required in order to facilitate insertion or removal of a disc from the turntable l5, and to enable the scanning arms 34 and 50 to be swung over totheir starting points at the outer edge of the disc. To

accomplish this, an operator or other attendant raises the outer end of the upper arm 34 a desired ,distance, with the pivotal bearing 35 as an axis of rotation, and by means of a cam 5'1, secured to the pivoted end of the upper arm, and a cam surface 59 on the lower arm 53, the lower arm automatically is cammed downwardly a distance just suiiicient to clear the disc. The configura Tzion of cam 58 is such that when the lower arm has been cammed downwardlyto clear the disc,

further upward movement of the arm 34 does not further depress the arm 59 but instead merely maintains th necessary clearance between the scanning head of the lower arm and the disc. Any lateral movement of arm 34 causes a cor responding movement of arm 53 and thus both arms may be positioned at any desired point with respect to the disc.

The lower arm carries an electrical contact spring 6| insulated from the arm, so that the free end of the contact spring slides across a rheo stat or potentiometer coil 52 during lateral movement of the scanning arms thereby to var the speed of the driving motor !8 in a manner to maintain substantially uniform linear scanning speed during a recording or reproducing operation, as hereinafter set forth. The spring 6! is sufii; ciently resilient to permit the arm 50 to be cammed downwardly the necessary distance to clear the disc whenever the upper arm 34 is raised. A leaf" spring 64 secured at one end to the bracket struc; ture 45, 46, assists in returning the arm 50 to its recording and reproducing position after it has been disengaged by the cam 51, the leaf spring also assisting in preventing downward movementf of arm 50 in excess of that caused by the cam f ming action of the cam'51. Y

The diameter of the recording and reproducing discs 25 employed may vary within considerable} limits, depending upon the number of spiral scanning rows per inch, the rate of linear s can, ning desired, and the length of the meszages to be transmitted. If, for example, the disc formed with fifty spiral recording rows per inch,

The outer end of arm 50 -a.x-'disc .2 18 finches .in :diameter -will izpermit linear subscribers sending station S, ac'entral receiving and retransmitting station C, :"and ta :receiving subscribersstation orabranchnfliceR. suitable transmitting unit .may be employed at station S and anysuitablerecording unitm'ay be employed at -station R, various of which units are well known inithe art. For example, and by Way of illustration only, the :transmitting unit may comprise a photocell pickup'device of a type heretofore employed .for scanning subject matter to be transmitted in facsimile, such as the scanning device shown 2,158,391, issued Maylfi, 1939. In general -such a. scanningunit comprises a drum 1.0 which carries the record sheet bearing the subiectimatter to be transmitted, the drum being rotated-at .a

predetermined constant speed by a synchronous u orother constant speed'motor -'H which is energized. from an alternating current power supply line l2. As is known, a beam of light .from a suitable light source 14 is focused, by-means. of a lens 15, on successive elementalareas of the subject matter blank being scanned, the beam being reflected from therecord sheet through a lens .16 to'a photocell 1-1. Alight ch'opperin the form of a disc 13 is interposed between the photocell 1 and the reflected scanning light. Preferably a second photocell 'lf8iis employed for obtaining picture inversion so that, as set forth in Wise-Patent No. 2,176,442,.issued October 1'7,

1939, the record as reproduced at the receiver will show dark portions when dark portions of the :subject matter to be transmitted .are scanned.

.As .is well known, thefimodulated carrier signals generated by the photocell, which are in accordance with .the subject matter-scanned by the transmitting unit, are amplified by an ampli'fier 19, the amplifier being connected by a transmission circuit Bil to a receiving .amjplifier 81in the central station C. A manually operable switch 82 is provided to enable the recording and reproducing unit 28 to be connected either to amplifier 8| of the incoming line or to'an amplifier Ill] of an outgoing circuit. In the "figure the switch is shown in position formeceiving an incoming message from the tiansrnittin'g station S. 'A transformer 24 .is'bridge'd across the output of amplifier 8!, this secondary winding of the transformer being connected in 'circuitwith asuitable signal device, such as a'neonlamp 83,

therby to call the attention of a central "orifice attendant to the fact that the sending station S has its'car'rier on and wishes'toltransmita"mes, sage. The carrier may have any-suitable 'fre quency, 'for example, 2500 cycles? In order that the central stationmay prevent transmission from the sending stationuntil 'a'dis'c 25 is in proper position for recording'a message, a 'control circuit is providedwhich comprises a source ofcurrent 86, a resistanc "and-a-manu in Wise Patent -No. w

ammuthrown the :right, Lth'e battery 86 is connected. to ra :midpoint .tap :of :a coil :89 that is bridged across :the iline flo- .A similar :coil .90 .is bridged across the *line .atthe transmitting :station is, and a midpoint tap from :the latter :tcoil is-zconnectedthrougharelay lliito ground. -i'Ihe.armature 92 and make contact of .relay .9! cnntrol i2 circuit which :includes a source of aenerrgizing current 94 and an electromagnet 595 :that controls the movement of the scanning .carriage of the =:pickup unit, generally in the manner :dis closed in Wise et a1. Patent No. 2,262,715,1issued November 11., 1941. As explained in the last-mentioned patent, the movable carriage which supports the photocell scanning :assembly is "advanced by a lead screw that propels the carriage at proper scanning speed when :it is engaged by "a half-nut, and the 'en'gagementand disengagement of the half-nut'is controlled :by electromagnet '95 so that when the el'ectromagnet is deenergized, scanning cannot proceed, "but when it 'is energized scanning is effected. 'Therefore, so long as switch 88 is not closed in the central oflice, transmission from station S cannot proceed, thus avoiding the possibility :of

. the attendant' at station S of the condition of the equipment. I

The driving motors at the transmitting andmeceiving stations should operate in synchronism and at the proper speed, and. a convenient way 'of insuring thisis illustrated inFig. l inwhishthe power supp1y 'l2 "for the transmitting station is extended, by means of conductors Si and ma-nually operable switch 28 to thedriving motor lil of the recording'and reproducing unit at the cen tral station. This is feasible when the station s is comparatively-close to the central station C,-or when .the'local power supply at' the central "station is synchronized. by the power company with thesupply at station S. In the illustrative embodiment shown, one side oi -the powercircuit i's connected by a conductor 99 through the field windin xof 'a universal driving motor '18 and thence through'the'armature off the motoncurrent limiting resistance H19, snap switch-s (ti he-n closed) 'and conductor liii to the other side-of the power circuit. Connected in shunt with the-armature is a "circuit which includes the sli'dable contact BI and resistance coil 52, the arrangement being such that as the arm 51: of =the unit traverses the disc 25 from the outermost spiral grooves 260; to the innermost spiral grooves 2%, the speed of the motor will be progressively increased thereby to maintain the lineal-scanning speed constant irrespe ctive-of the' diameter of tha't portion of the disc at the time being scanned. mar examplewhen the outermost rows of an 18 inch discarebeing scanned, the disc should be rotated at a speed-of the order of'73R. PsMfiinord'erto give thedesi'red linear scanning rated 6 feetper second, whereas when the innermost rows 2Gb are being scanned the speed of the disc should be of'ithe order'of"228 R. P. If a '16- inch disc were employed, "the rotational speed or the disc, when the outer rows'are being scanned woiild'be oftthe order of85 R. 1 M. Theresis'tance coil 62 has a portion [93 whichisconnectedby aconductor H14 'to the other side of the armature of motor-18 so as to insure that the proper amount of resistance will bein circuit atthe beginningaof.

"ally'operable switch 88. When the switch a scanningoperation :by:the'reproducer headfiztr The resistances B2 and I03 act as a shunt across the armature of the motor, and are proportioned so that with the arm 50 in the starting position the correct linear scannin speed will be obtained, and as contact BI is moved to the left, as viewed in Fig. '7, the resistance of the shunt increases and causes increase in the voltage across the armature thereby increasing the motor speed at a rate to maintain the linear scanning speed approximately constant.

The switch 8 is provided to insure that the recording unit will be stopped automatically at the proper time, that is, when the innermost rows 26b of the disc have been reached. As seen in Figs. 1 and 3, the bracket portion 45 of the swinging arms has a stud or pin I3i rigidly secured thereto. When the arms are swung over -to the starting position, the stud I01 engages a rigid stop pin or stud I30 to determine the proper starting position for a given size of disc, and as scanning proceeds and the inner rows 2% are reached, the stud I3i engages and depresses a spring member 132 and causes operation of the snap switch s in order to open the motor energizing circuit and stop the recording and reproducing unit before the scanning head has passed the last or" the innermost rows 2%. It is to be understood that any other suitable means for controlling the speed of the driving motor I8 and for controlling the starting and stopping of the recording and reproducing mechanism may be employed. When a recording has been effected on the disc 25, the switch 88 is thrown to the left, i. e., the position shown in Fig. 7, which prevents further transmission by the sending station S.

Retransmission of the recorded message at station C is eiiected by throwin switch 82 to the extreme right, thereby to connect the reproducing head 28 to the outgoing amplifier III], and the motor I8 again is started by closing the switch 08. After passing through amplifier III], the modulated carrier comprising the message passes through the band pass filter H I and thence over line II2 to the band pass filter I I4 at the receiving station R. From the filter II4 the message passes through the demodulator H5 after which the demodulated signals are amplified by anamplifier H6 and applied to a recording stylus II'I that records in facsimile the received message on a receiving blank carried by the recording drum II8. Recording may be effected in any suitable manner, for example, as on an electrosensitive recording blank of the character disclosed in Wise Patent 2,294,146, issued August 25, 1942; Kline Patent 2,251,742, issued August 5, 1941; or Kline et al. Patent 2,294,149, issued August 25, 1942. If it is desired to employ a percussive type recorder, thereby to obtain a recorded black and white copy from which other copies may be made by mimeograph, hectograph and other printing processes, the receiving apparatus may be in accordance with OBrien et al. Patent 2,260,862, issued October 28, 1941, or dHumy et al. Patent 2,301,024, issued November 3, 1942. Additional control circuits between the transmitting station S and the central station C, and between the central sta tion and the receiving station R, may be em ployed, various of which circuits are shown in the patents hereinbefore referred to. p

The underside of the disc 25 may be employed either for the recordation and retransmission of another message or for storing synchronizing signals to insure that the driving motors at the sendmg and receiving stations will operatein syn chronism. and in rr p p a e. relaiiquwithr z comprises a sixty cycle alternating current,"

through resistances I00 and I01 so that, when switch I08 is thrown to the left, as viewed in Fig.'

'7, the alternating current, usually sixty cycles, which drives the transmitting motor II at the sending station will be recorded, by means of reproducer head 28', on the underside of disc 25 simultaneously with the recordation of a message on the upper side thereof. When retransmitting from the central station, switch I08 is thrown to the extreme right, and the recorded alternating current signals are transmitted to an amplifier I2 I after which they pas to a modulator I22. In' the modulator a source of carrier current of suit-I able frequency, for example, 4000 cycles, is modu-' l'ated by the sixty-cycle alternating current and the modulated carrier passes through a filter I23 to the outgoing transmission line I I2. At the receiving station R. this modulated carrier is received by the band pass filter I24 and passed to a demodulator I25. The demodulated sixty-cycle current is amplified by an amplifier I20 and applied to the driving motor I I0 of the recorder unit, thus insuring that motor II9 will always operate in synchronism and in proper phase relation with respect to the transmitting motor II of the sendin station S.

After retransmission of the signals stored on the disc 25, it is desirable to erase the signals, whereby each disc may be used over and over again. This may be eiiected by providing erasing magnets similar to magnets 28 and 28, which erasing magnets may be disposed immediately be hind the recording and reproducing magnets and energized as retransmission is effected to erase the message signals as soon as they have been retransmitted. Such erasing magnets conveniently may be carried by the arms 34 and 50 generally in the manner of magnets 20 and 28, it being understood that a suitable source of erasing current is applied to the erasing magnets at the proper times. I, Also, and as shown in Fig. '2, the magnets 28 and '28 may be employed as erasing magnets. In this case, when the recordedsignals have re transmitted, the switches 82 and I08 are moved to their midpoint positions, thereby disconnecting the magnets from the incoming and outgoing circuits. Switch I05 is then closed and supplies a source I5I of erasing current to both sets of magnets as the disc 25 is rotated and scanned by the magnets. Preferably, a source of alternating cur rent having a frequency of the order of 30,000 cycles is employed as the erasing current.

Figs. 5 and 6 of the drawings show a modified form of recording and reproducing disc. In this, case a disc I40 has secured to the upper and under surf-aces thereof a ridge formed by a spiral ribbon MI and MI of good magnetic properties; The edge of the ribbon adjoining the disc I40 may be secured thereto in any suitable manner, as by spot welding or otherwise, and the adjacent turns of the ribbon preferably are sepa-'- rated by a ribbon I43 which is of smaller width than ribbon MI, and which forms a vale and also a track for the scanning head. Ribbon I43 may comprise either magnetic material or nonmagnetic material such as brass, and it maybe spot welded or otherwise secured to the base of disc I40. It will be understood that the signals are magnetically stored in the ridge formedby t tru ed e. eer ns i. ribb n an 9F.-

Ill. Thi construction has the advantage of lower cost than that in which the disc is out or ooved in the manner of the disc of Fig. 4. The

operations of recording and reproducing are effected in the same manner as heretofore explained with respect to disc 25.

In each of the modifications of the recording and reproducing discs shown herein, it is preferable that the diameter of' the innermost row 261) be sufliciently great to avoid the necessity of rotating the disc at undesirably high speeds in order to maintain a desired linear scanning rate. It will generally be found that the diameter of the innermost row conveniently may be of the order of six inches. The blank space in the central portion of the disc may be employed for receiving stickers or identifying labels on which the designation of the sending and receiving stations may appear, or such stickers and labels may contain routing instructions or other information desired by the operator or attendant at the central station.

While the invention has been described and explained in detail in connection with specific illustrative embodiments thereof, it is to be understood that the invention may be embodied in other forms and that it is not limited except as indicated by the terms and scope of the appended claims.

What is claimed is:

1. Facsimile recordin and reproducing apparatus comprising a rotatable disc having on each side thereof a spiral ridge of magnetizable material and a spiral vale on either side of said ridge, a recording and reproducing head for each side of said disc and each comprising an electromagnet responsive to incoming signals and having a pole piece for scanning successive areas of the adjacent spiral ridge and locally magnetizing selectable areas thereof as said disc is rotated, means for rotating the disc, a first scanning arm for carrying one of said recording and reproducing heads and a second scanning arm for carrying the other of said heads, means for mounting said arms so that they move in synchronism with each other for scanning both sides of the disc simultaneously, and means controlled by one of said scanning arms for continually increasing the rotational speed of said disc as scanning of the disc proceeds from the outer portion thereof to the inner portion thereof.

2. Facsimile recording and reproducing apparatus comprising a rotatable disc having the opposite faces thereof composed of magnetizable material, a recording and reproducing head for each side of said disc and each comprising an electromagnet responsive to incoming signals and having a pole piece for scanning successive areas of the adjacent face of the disc and locally magnetizing selectable areas thereof as said disc is rotated, means for rotating the disc, a first scanning arm for carrying one of said recording and reproducing heads and a second scanning arm for carrying the other of said heads, means for mounting said arms so that they move in synchronism with each other for scanning both sides of the disc simultaneously,

means for simultaneously applying different sources of incoming signals respectively to the two recording and reproducing heads, and means controlled by one of said scanning arms for progressively varying the relative rotational speed between said pole pieces and the disc as spiral scanning of the disc proceeds from one diametral portion thereof to another portion thereof of different diameter.

3. Facsimile recording and reproducing apparatus comprising a rotatable disc having the opposite faces thereof composed of magnetizable material, a recording and reproducing head for each side of said disc and each comprising an i1 electromagnet responsive to incoming signals and having a pole piece for scanning successive areas of the adjacent face of the disc and locally magnetizing selectable areas thereof as.

said disc is rotated, means for rotating the disc, a first scanning arm for carrying one of said 1 recording and reproducing heads and a second scanning arm for carrying the other of said heads, means for mounting said arms'so that they move in synchronism with each other for scanning both sides of the disc simultaneously, means for simultaneously applying different sources of incoming signals respectively to the two recording and reproducing heads, means including said heads for subsequently reproducing simultaneously the signals thus stored on opposite sides of the disc and separately applying them to different outgoing circuits respectively, and means controlled by one of said scanning arms for progressively varying the relative rotational speed between said pole pieces and the disc as spiral scanning of the disc proceeds from one diametral portion thereof to another portion thereof of different diameter.

FERNAND E. DHUMY.

RALEIGH J. WISE.

REFERENCES CITED The following references are of record in the file of this patent:

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